Electric furnace and resistance element therefor



W, E. MOORE June 27, 1933.

ELECTRIC FURNACE AND RESISTANCE ELEMENT THEREFOR Filed Oct. 19, l93l 2Sheets-Sheet 1 June 27, 1933. 'W M ORE 1,915,747

ELECTRIC FURNACE AND RESISTANCE ELEMENT THEREFOR Filed Oct. 19, 1931 2Sheets-Sheet 2 fig .5

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Patented June 27, 1933 PATENT OFFICE MOORE, OF PITTBBUM'H, PENNSYLVANIA,ASSIGNOB T PITTSBURGH RESEARCH CORPORATION, OF PITTSBURGH, PMSYLVANILnnncmc rumucnann RESISTANCE We 'rnnanron Application flledoctober 1B,1931. Serial No. 589,798.

My invention relates to improvements in electric furnaces, and moreparticularly to a furnace for heat treatment of metals, although notnecessarily restricted to this use.

Heretofore in the operation of furnaces of this character, repairing ofthe furnace or of the resistance elements therein necessitate aconsiderable loss oftime due to the fact that the furnace must cool downbefore workmen can enter it to make repairs. I

propose to overcome this difficulty by providing a resistance elementwhich may be removed with the roof'of the furnace, thereby effecting asaving in the time required for repairing the furnace and resistanceelements.

Another object of my invention is to provide a novel resistance elementand-novel supporting means therefor.

-2'0 Otherobjects and advantages of my invention will be apparent duringthe course of the following descri tion.

In the accompanying rawin swhich form a part of this specification anwherein like characters of reference denote like parts throughout thesame, v Figure 1 is a vertical transverse sectional view through afurnace embodyinginy invention.

" Figure -2 is a longitudinal sectional viewtherethrough, Figure 3 is afragmentary horizontal se tional View. showing one form of'resistanceelement,

Figure 4 is a similar 'view showing another form of resistance element,I

, Figure 5 is a detail elevation of a furtherform of resistance element,

Figure 6 is a similar view of still another form of resistance element,and,

Figure 7 is a detail of a still further form I preferably arranged inthe same plane, and

of resistance element.

In the drawings, wherein for the purpose of illustration is shown apreferred embodiment of my invention, the numeral 10 designates a heattreating furnace hood arranged over the stationary base 11. The hood 10is provided with a removable roof 12, and

the entire hood is lifted. on and off the base by meansof the usual shopcrane. The usual are arranged exteriorly of the roof and exfurnace hoodis provided with an interior shoulder or shelf adjacent its lower endwhich extends towards the furnace base. This shoulder collects scale,dust and dirt, and therefore must be cleaned at regular intervals. Inorder to obviate this difficulty I have provided the shelf 13 with-asubstantial slope towards its inner edge as seen in Figures 1 and 2.,With this arrangement debris will slide off the shelf when'the hood israised, thereby rendering the shelf self clean mg. In the usual furnaceof this type the electric heating elements are supported onand securedto the side walls of the furnace hood. In my invention the electricheating elements are supported entirely by the removable roof 12; andare removed therewith when the roof is lifted from the hood 10. A

A series of heat resistant metal rods 14 70 carry stirrups 15 at theirlower-ends, and project upwardly through bushed openings in thebrickwork of the roof arch, pass through bearing plates 16 and are heldin the bearing plates by nuts 17 enga%ug the screw threaded ends of therods. ach of the stirrups 15 carries an insulating, resistor supportingspool 18. Theresistor comprises a strip orribbon '19 which asses overthe spools 18,and.depends there m in a series of loops which are spacedfrom the walls of the hood 10 and extend to a point adjacent the shelf13. The ends of the resistor elements are connected to terminals 20which tend through the same. Various distributions of the resistor maybe effected b lengthening some of the rods 14 and there y shortening thecorresponding. resistor loop, as seen in Figure 2. Y Y I The lower endsof the resistor loops are a difierent vertical distribution of theresistor loops is desired, it is only necessary to change some of therods 14 in contrast to the old method which required tearing down thewalls of the furnace to'replace the resistor supports. I Z

Due to the fact that the rods 14 are in tension; they may have a smallcross section, and the heat conductivity from the interior of thefurnace through the roof'arch will conse-' quently be reduced to aminimum. When the roof with its resistor loops is lowered onto thefurnace hood, the loops are guided into position b the T-headed bolts21.

While t e usual flat ribbon resistor may be used, I prefer to use aresistor strip or ribbon which has been passed throu h a cor rugatingroll or the like and has a ished or channeled cross section, as seen inFigure 3. This shape of heater element has reater 4 strength than a flatribbon due to the ateral stiffness im arted by the dishing feature, andat a very s lght increase in cost. Where the dished ribbon passes overthe spools it has a tendency to flatten out.

. In place of the dished form shownin Figure 3, the resistor element maybe passed ive through corrugating rolls which will -shaped crosssection, as shown in igit an ure 4. Y

In Figure 5 I have shown another modification of the resistance' elementin which it is twisted into an auger shape to form a resistor which willequally expose its surface to the furnace interior. I

In Figure 6 the flat resistance element is I wound into a helix of arelatively small diameter to increase the effective heating surface ofthe resistor.

In Figure 7 the resistor 19 is bent into alternate loops 22 vlongitudinally and transversely of t e resistor strip to strengthen theresistor and to increase the exposed heating surface by its doubledcorrugated efiect.

While I have shown and described the preferred embodiment of myinvention it isto be understood that various changes in the size, shapeand arrangement of parts may be resorted to without departing from thespirit of my invention or the scope of the subjomed claims.

Having thus described my invention, what I claim and desire to protectby Letters Patcut is:

1. In a heat treating furnace, a base, a removable hood adapted to beplaced over said base, electric heating elements arranged in proximit tothe wallsof said hood, and a sloping s elf arranged about the interiorof the hood beneath the heating elements.

2. In a heat treating furnace, a furnace hood, a removable rooftherefor, a resistance elementv supported by said roof and adapted toextend a substantial distance down into said furnace hood, and guidemembers secured to said furnace hood for said resistance element,whereby the resistance element may be removed from the hood with saidroof.

3. In a heat treatin furnace, a furnace hood, a removable roo therefor,an electric resistance element supported bysaid roof and extendingjdown'into said furnace hood in' proximity to the walls thereof, and guidesupports for said resistance element arranged on the walls of thefurnace hood, whereby said resistance element is removable with said rooY 4. In a heat treating furnace, a furnace body, a removable rooftherefor, resistance supports secured to said roof, an electricresistance element carried by said suplpgrts and extending down intosaid furnace dy, and guide members for said resistance element securedto the walls of the furnace body.

5; In a heat treating furnace, a' furnace, body, a removable rooftherefor, a resistance ribbon for said furnace, and means carried bysaid roof to support said ribbon in loops of different lengths whichextend down into said furnace b0 6. In a heat treating furnace, afurnace furnace, a furnace 9 y, a removable roo therefor, a plurality ofresistance supporting members depending from said roof, said membersbeing of vary ing length, means .at the ends of said members forsupporting a resistance element which extends down into the furnace, and

means on the walls of the furnace body for guiding the lower end of theresistance element.

9'. In a heat treating furnace, a furnace hood, a removable rooftherefor, a plurality 11 v of resistance supporting elements dependingfrom said-roof insulatin spools carried by the ends of said supportingelements, a resistance stri su ported by said spools and depending t ererom in spaced loops which .120

extend. down into the furnace hood, means in said furnacehood forguiding the loops of resistance, and terminal members in said roof forthe resistance strip.

10. In a heat treat hood, a removable roo therefor, a plurality ofsupporting elements .of varying lengths 'depending'from said roof,insulating furnace, a furnace s ools carried b the ends of said suportin of y ted on said 1 0 ements, ,a resistance strip supper tricresistance element comprising a strip of resistance material twistedinto an auger shape and arran ed in a series of spaced loops in thefurnace, t e overall Width of the auger shaped element beingsubstantially equal to the width of the strip from which it is formed.

In testimony whereof I affix my signature.

WILLIAM E. MOORE.

